Another repost of a comment on The Passive Voice.

The phrase ‘purple prose’ goes back to Horace’s Ars Poetica; and in Horace’s time, purple dye was a rare luxury, and purple was the colour of kings. He objected to ‘purple patches’ not because they were rich or ornate, but because they were patches and did not match the fabric of the whole story. Here is a translation of the passage in which he coined the phrase:

Your opening shows great promise, and yet flashy purple patches; as when describing a sacred grove, or the altar of Diana, or a stream meandering through fields, or the river Rhine, or a rainbow; but this was not the place for them. If you can realistically render a cypress tree, would you include one when commissioned to paint a sailor in the midst of a shipwreck?

You can see that it is extraneous purple that he objects to, and not purple per se.